A number of different types of storage hardware are now in use. These include sequential-access storage elements, such as shift registers and First-In-First-Out (FIFO) buffers, from which data are accessed in a particular order. Random-access storage elements, such as semiconductor random access memory (RAM), are also commonly used and differ from sequential-access storage elements in that they allow data to be accessed in any order. Some types of memory, such as burst-mode memory, combine attributes of both sequential and random-access memory. A few more complex hardware designs are also in use, such as Content-Accessible Memory (CAM) in which the contents of at least part of the memory itself can be used to access particular storage locations. Electrical engineers have used these types of storage in a wide variety of hardware systems, and software engineers have used them to manage more complex data structures, such as linked lists or trees.